Method and coring for casting and manufacturing cylinder heads and the like



2, .965 v. E. SCHAFER, JR 3,167,854

METHOD AND CORING FOR CASTING ANDMANUFACTURING CYLINDER HEADS AND THELIKE Original Filed April 2, 1957 3 Sheets-Sheet 1 INVENTOR. 2

ATTOzP/VEV 196:) v. E. SCHAFER, JR 6 METHOD AND CURING FOR CASTING ANDMANUFACTURING CYLINDER HEADS AND THE LIKE Original Filed April 2, 1957 3Sheets-Sheet 2 A TTOANf V- Feb 2, 1965 Original Filed v. E. SCHAFER, JR\3,167,854 METHOD AND CORING FOR CASTING AND MANUFACTURING CYLINDER HEADSmomma LIKE April 2, 1957 3 Sheets-Sheet '3 INVENTOR ATTORNEY UnitedStates Patent METHGD AND (IQRING FOR (IASTING AND MANUFACTURING CYLINDERHEADS AND THE LIKE Vernon E. Schafer, .lr., Livonia, Mich assignor toGeneral Motors Corporation, Detroit, Mich, a corporation of DelawareOriginal application Apr. 2, 1957, Ser. No. 650,249, new Patent No.2,893,371, dated July 7, 1959. Divided and this application Oct. 30,1958, Ser. No. 770,704

17 Claims. (Cl. 29-4564) This invention relates to a method of formingan expansion joint in a member of a thermal device having a limitedsurface portion thereon subjected to rapid and extreme cyclic changes ofsurface temperature thereby subjecting said surface portion to severecyclic thermal expansive and contractive conditions relative to theother surface and interior portions of the member and has particularapplication to internal combustion engines and the like. This is adivision of my copending United States patent application S.N. 650,249,filed April 2, 1957, and entitled Expansion Joint, now Patent No.2,893,371, issued July 7, 1959.

The various surfaces defining a combustion chamber or cylinder of aninternal combustion engine are subjected to rather severe cyclic thermalconditions due to the extremely rapid changes in temperature alternatelyimposed on these surfaces by the heats "of compression and combustionand by the flow of relatively cool gaseous charges into the cylindersduring the engine operating cycle. These changes in surface temperatureresult in the cyclic imposition of expansive compressive and contractivetensive stresses on these surfaces and the immediately adjacent layersof the various cylinder-defining members. In time these cyclic stressesresult in fatigue cracking of these surfaces. Such cracking generallyoccurs intermediate and adjacent ports or openings in such members wherethe surface layer subjected to such cyclic stressing is of reduceddimension. Such cracking is also particularly prevalent in thoseapplications where the engine is subjected to excessive fluctuations inload and speed; factors which result in sudden applications ofrelatively cool incoming air onto overheated cylinder-defining surfaces.

This invention contemplates providing the combustion chamber surfaces ofa thermal device of the type described with expansion joints similar infunction to those provided by the shallow grooves shown and described inUnited States Patent No. 2,791,989 issued to John Dickson and entitledInternal Combustion Engine. In accordance with the invention, suchexpansion joints are formed by casting inserts of nonfusible materialinto the cylinderdefining members adjacent critical areas. The resultantcastings are machined so that these inserts intersect the combustionchamber surface and extend through the layer of the member normallysubjected to such cyclic expansive and contractive thermal conditions.Under engine operating conditions the initial expansive compressionimposed on this surface layer stresses this layer beyond its compressiveyield point for the temperatures involved and effects the formation ofgrooves immediately adjacent to and including the opposite sides of theinsert. These grooves serve to accommodate and isolate subsequentexpansion and contraction of the surface layer from the adjacent FIGURE1 is a fragmentary view of a cylinder for an internal combustion engineof the unifiow Diesel type with par-ts thereof broken away and inlongitudinal section to show a cylinder head such as may be formed inaccordance with the invention;

FIGURE 2 is a fragmentary view taken substantially on the line 22 ofFIGURE 1 and shows a portion of the underside of the cylinder head inelevation;

FIGURE 3 is an enlarged fragmentary sectional view taken substantiallyon the line 3-3 of FIGURE 2;

FIGURE 4 is a view similar to FIGURE 3 and taken substantially on theline 44 of FIGURE 2;

FIGURE 5 is a perspective view of one form of insert shown in theembodiment of the invention of FIGURES 2-4;

FIGURE 6 is a perspective view of a second form of insert as used in theembodiment of the invention of FIGURES 24;

FIGURE 7 is a perspective view of a modified form of insert adapted foruse in place of the insert shown by FIGURE 6; and

FIGURES 8, 9 and 10 are views showing the method of casting andmachining a cylinder head to include expansion joint inserts inaccordance with the invention.

Referring more particularly to the drawings, FIGURE 1 shows a portion ofa uniflow, two-cycle diesel engine in which a cylinder bore 10 in anegine block 12 reciprocably mounts a piston 14. The piston forms anexpansible combustion chamber 16 with a cylinder head 18 secured to theengine block and closing the cylinder bore at its upper end. Thecylinder head is cored to provide coolant passages 20 and two exhaustpassages 22. The exhaust passages 22 terminate in two ports 24 openingon the combustion chamber or fire deck surface of the head indiametrically flanking relation to an opening 2s provided therein forthe nozzle of a fuel injector 28. The exhaust ports 24 are counterboredto receive annular inserts which are beveled to seat the heads of twoexhaust valves 32 reciproca-bly mounted in the head.

As indicated above, the combustion chamber or fire deck surface of thecylinder head of such an engine is particularly susceptible to surfacecracking intermediate and adjacent the valve ports and injector nozzleopening. The cracking which occurs intermediate the injector opening andthe exhaust ports is generally in a diametrical plane common to theseveral openings. The expansion and contraction of the fire deck surfaceparallel to this common diametrical plane also tends to develop sunbursttype cracking of the fire deck surface radially out wardly from theexhaust ports transversely of this common diametrical plane. After suchcracks are initiated in the fire deck, they tend to progress through thefire deck and in time may result in the leakage of coolant into thecombustion chamber. Such cracking and the subsequent cyclic expansionand contraction of the adjacent combustion chamber surfaces also resultin the oval izing of the injector and valve seating surfaces withattendant Wear and malfunctioning of the injector and valves.

As shown in FIGURES 2-4, inserts 34 and are cast into the cylinder headin accordance with the invention and serve to isolate the cyclicexpansion and contraction of the combustion chamber surface from thecritical areas intermediate and adjacent to the injector opening, thevalve ports and other openings through the fire deck of the cylinderhead. These inserts are of a material or are coated to prevent fusionwith the molten metal during the casting process. They are also oflimited mass to prevent chilling of the adjacent portions of thecasting. It has been found that these inserts can be of either a metalor ceramic-type material having a high fusion temperature or may be of ametal and coated with an oxide, ceramic or metallic material providingsuch fusion-resisting char- '2 m9 acteristics. In the illustrativeembodiments these inserts are first stamped from rolled sheet steel andare then coated by dipping in a molten aluminum bath which is followedby a diffusion heat treating process in the manner shown and describedin the United States Patent 2,569,097. This provides a coating of ahighly temperature resistant iron-aluminum compound.

In the illustrative embodiments the inserts 34 and 40 are arranged inpairs in parallel spaced relation flanking the critical areasintermediate and adjacent to the injector and valve port openingsthereby serving to isolate the cycle expansion and contraction of theremainder of the combustion chamber surface from these critical areas.The inserts 34 and 4% each have corrugated portions and 41,respectively, normal to and intersecting the surface layer of the firedeck which defines the combustion chamber and is subjected to the cyclicthermal conditions. The corrugations in the inserts extend parallel tothe combustion chamber surface and interlock with the adjacent surfacesof the cylinder head. By using such corrugations it has been found thatsuch inserts can be used without increasing the thickness of the firedeck inasmuch as the interlocking serrated surfaces carry thecompression and combustion loads imposed on the adjacent portions of thefire deck.

The inserts 34 and 40 are terminated inwardly of the fire deck fromtheir corrugated portions by rounded or cylindrically looped portions.These looped portions are open lengthwise to permit the free flow ofmolten metal within the loop during the casting process and serve toterminate the cracks formed in the head by the use of such inserts. Theinserts 34 each have a single looped portion 36 which extends inparallel spaced relation to the combustion chamber surface andintersects the counterbores for the valve seat inserts at its oppositeends. The inserts 4t? are each rounded to provide two cylindrical orlooped portions 42 and 43 formed at right angles to each other. Thelooped portion 42 is normal to and intersects the combustion chambersurface at one end and the looped portion 43 extends in parallel spacedrelation to the combustion chamber surface and intersects the adjacentvalve seat insert counterbore at its end opposite the looped portion 42.

Under normal engine operating conditions, the cyclic expansion of thesurface layer of the head adjacent the combustion chamber effects theformation of grooves 37- and 44 immediately adjacent the inserts 34 and40, respectively. Since the compressive stresses resulting from suchcyclic expansion exceeds the yield points of the insert and headmaterials at the temperatures involved, these grooves are formed in partby the outward extrusion of a portion of the insert and in part by thepermanent upsetting of the adjacent surface layer. The grooves 37 and 44are thus formed during the initial or breakingin period of engineoperation to the depth of this surface layer subjected to cyclic thermalconditions and are adapted to accommodate subsequent expansive andcontractive plastic flow of this surface layer without imposing furthercompressive and .tensive stresses on. the critical areas of the headintermediate the inserts.

While the illustrative embodiments of the invention show the use ofpaired inserts in flanking relation to the critical the deck surfaces,satisfactory results have also been obtained using single insertsbiseeting such critical surfaces. In certain engines and particularlythose of larger size, additional inserts have also proven advantageousin preventing cylinder head cracking. In certain engines andparticularly smaller engines where radial suburst type cracking from theexhaust port openings is not a problem, inserts in the fire decktransverse to the diametrical plane of the valve axes may not benecessary. Other forms of nonfusible inserts also are contemplatedwithinthe scope of'the invention and may be highly desirablein certainengines since the design and location the inserts within the headcastingproper.

of the inserts should be related necessarilyto the prob lems derivingfrom the cyclic thermal conditions imposed on the surfaces of thevarious engine members.

A third form of insert 45 is shown in FIGURE 7. This insert istriangular in shape and particularly'designed for use in applicationssimilar to that for which the inserts at) are used in theabove-described embodiment. As shown, the insert 45 has a portion46'correspending to the portion 41 of insert 49 and having corrugationsintended to provide interlocking surfaces parallel to the combustionchamber surface of the fire deck. A round bead 47 is formed arcuatelyand diagonally of the corrugations and is adapted to terminate theinsertcreated crack; intersecting the exhaust port at one end and thesurface of the combustion chamber at its other end. The insert 45 may bemade of a pressure and heatformed asbestos or other suitable nonmetallicmaterial, as shown, or may be of a suitably coated metallic sheetmaterial similar to that used in the above-described embodiment.

A preferred method of casting and forming a cylinder head to includesuch inserts is shown in FIGURES 8, 9 and 10. Referring to FIGURE 8, thevarious members of the head mold are formed separately and include aslab 5t) of baked core sand which forms the lower half of the head mold.The upper face 52 of this core slab is adapted to mount and referencecores for water, gas and other passages within the head. Such scores forexhaust gas and .water passages are indicated at 54 and 55,-

respectively. A plurality of grooves 56 are formed in the core slab andopen on its upper face, being arranged in appropriate patterns withrelation to the various core mounting positions. These grooves arebeveled, as. indicated at 58, adjacent the upper face of the core slaband are adapted to mount the various inserts to be cast into thecylinder head. Prior to their insertion in the mounting grooves, theportion of each insert intended to extend within its mounting groove iscoated with a suitable mounting paste. Upon insertion in the groove'anyexcess of this paste which is designated by the referencenumeral 6b isretained within the beveled portion of the groove thus preventing anyblow-hole inclusions of the paste within the head casting proper. .Thisbeveled portion of the groove also serves to insure thatthe moltenmetal, having convex meniscus characteristics with relation to thenonfusi'ble insert, will not leave any pockets adjacent When the insertshave been mounted-in their. respective grooves, the various cores aremounted on the slab core in their proper positions. An upper mold half,not shown, is then clamped to the slab core to complete thehead mold.After the mold has been thus assembled, the head 18 is cast by pouringmolten metal in the mold. After the casting operation, the mold membersare removed in a conventional manner, leaving the resultant head castingas shown in FIGURE 9. The casting is then cleaned and subsequentlymachined in the usual manner to' the finished fire deck surfaces andvalve seat insert counterbores as shown in FIGURE l0g'the metal removedbeing indicated by phantom lines. These machining operations, of course,insure that these inserts intersect these finished surfaces of the head.

From the foregoing description it will be obvious to those skilled inthe art that various changes might be made in the'preferred method ofcasting and forming the thermal device member to include non-fusibleexpansion joint'inserts, in the materials and shapes of the inserts andin the core mounting location, spacing and number of inserts utilizedwithout departing from the spirit of steps-of forming mold membersincluding aicore slab adapted to form combustion chamber end wallportions and to mount and reference core assemblies for providingpassages and contours Within said head and having a plurality of groovestherein adapted to mount said inserts in predetermined spaced relationto said core assemblies, the side walls of each of said grooves beingchamfered adjacent the mold face of said slab; mounting oneend of eachof said inserts within one of said grooves and projecting outwardlytherefrom, mounting said core assemblies with reference to said slabcore and said inserts; assembling said mold members to form a mold;casting said head by pouring molten metal into said mold with convexmeniscus flowing of the molten metal around the inserts within thechamfered portions of said grooves; removing the mold members from theresulting head casting; and subsequently machining said casting toprovide finished combustion chamber surfaces by removing a portion ofthe metal formed adjacent said slab core and including the portions ofsaid inserts projecting Within the mounting grooves during the castingprocess.

2. A method of manufacturing cylinder heads as defined in claim 1including the further step of subjecting the finished surfaces of saidhead intersected by said inserts to cyclic thermal conditions therebyeffecting the formation of grooves immediately adjacent the severalinserts by the compressive upsetting of the layer adjacent said surfacesubjected to such cyclic thermal conditions.

3. A method of manufacturing a cylinder head for an internal combustionengine having a plurality of nonfusible inserts cast therein comprisingthe steps of forming mold members including a slab adapted to formcombustion chamber end wall portions of the head and to mount andreference core assemblies for a plurality of passages and contourswithin the head and having a plurality of grooves therein adapted tomount said inserts adjacent certain of said core assemblies, the sidewalls of each of said grooves being chamfered adjacent the mold face ofsaid slab the immersion of each insert in a mounting paste to a depthsubstantially equal to the unchamfered depth of said grooves; insertingthe paste immersed end of each insert into one of said grooves; thereferencing and mounting of said core assemblies with respect to saidslab and inserts; assembling the mold; casting said head by pouringmolten metal into said mold with convex meniscus flowing of the moltenmetal around the inserts Within the chamfered portions of said insertmounting grooves; removing said mold members and said core assembliesfrom the casting; and subsequently machining said casting to providefinished surfaces by removing a limited portion of the metal formedadjacent said slab and the portions of said inserts projecting withinthe mounting grooves during the casting process.

4. A method of manufacturing cylinder heads as defined in claim 3including the further step of subjecting the finished surfaces ofsaidhead intersected by said inserts to cyclic thermal conditions therebyeffecting the formation of grooves immediately adjacent the severalinserts by the compressive upsetting of the layer adjacent said surfacesubjected .to such cyclic thermal conditions.

5. A member of a mold for casting a cylinder head for an internalcombustion engine comprising a slab having one face thereon adapted tomount and reference core assemblies for water, gas and other passagesand cooperative therewith to form the combustion chamber end Wallportions of the head casting, said slab having a plurality of groovesopening on said one face and having a desired predetermined orientationwith respect to the core mounting locations associated With said oneface and said grooves being adapted to mount inserts of nonfusible sheetmaterial to be cast into said cylinder head and being beveled adjacentsaid one face to receive a convex meniscus flowing of molten metalaround said groove mounted nonfusible inserts.

6. A member of a mold for casting a cylinder head for an internalcombustion engine comprising a slab having one face thereon adapted tomount and reference core assemblies cooperative therewith to form thecombustion chamber end wall portions of the head casting and Water, gasand other passages Within said head, said slab further having aplurality of grooves opening on said one face and arranged in spacedrelation to the core mounting locations provided on said one face andthereby to the passages to be formed by said core assemblies, saidgrooves being dimensioned to receive and support projecting inserts ofsheet material adapted to be nonfusibly cast into the cylinder head andsaid grooves being of an increased opening width adjacent said one face,the increased opening Width of said grooves being adapted to receivelimited fiow of molten metal Within each groove opening around thenonfusible insert mounted in each groove.

7. A mold assembly for casting a cylinder defining member for aninternal combustion engine including a first mold member of baked coresand, said first mold member mounting and referencing a plurality ofsecondary core sand members cooperative therewith to form combustionchamber end Wall portions and to define Water, gas and other passageswithin said cylinder defining member, said first mold member furtherhaving a plurality of grooves opening on at least one face thereof inpredetermined spaced relation to the passages to be defined by said coreassemblies and to each other, said grooves being dimensioned toremovably mount inserts of sheet material adapted to be nonfusibly castinto said cylinder defining member and the openings of said grooves tosaid one face of substantially greater width than said inserts andadapted to receive molten metal flow into said grooves during castingand around the groove mounted inserts.

8. A mold for casting a member having a surface thereon adapted to besubjected to extreme thermal conditions capable of inducing plastic flowtherein adjacent said surface, said mold including a mold member havinga face thereon adapted to define said surface, said mold member having aplurality of grooves therein opening on said one face in spaced relationto each other and adapted to mount inserts of nonfusible sheet materialto be cast into said member to intersect and limit the thermally inducedplastic flow of said surface between said inserts, and said groovesbeing beveled adjacent said one face to receive a convex meniscus flowof molten metal around said surface intersecting nonfusible insertsduring the casting of said member.

9. A mold for casting a member having a surface thereon adapted to besubjected to extreme plastic flow inducing thermal conditions, said moldincluding a mold memher having a face thereon adapted to define saidsurface, said mold member having a first plurality of grooves thereinopening on said one face in spaced parallel relation to each other, saidmold member having a second plurality of grooves therein opening on saidone face in space parallel relation to each other and extendingtransversely of said first grooves, and said first and second groovesbeing beveled adjacent said one face, the nonbeveled portions of saidgrooves being adapted to paste mount inserts of nonfusible sheetmaterial to be cast into said member to intersect said surface and limitthe thermally induced plastic flow thereof between said inserts, and thebeveled portions of said grooves being adapted to receive excess insertmounting paste and convex meniscus flow of metal around said insertsduring the casting of said member.

10. A method of manufacturing a cylinder head for an internal combustionengine comprising the steps of first casting said head to include atleast one insert of nonfusible sheet material intersecting a combustionchamber defining surface of said head; subsequently machining saidcasting to remove a portion of the cast surface metal and of each insertto provide a finished combustion chamber surface; and the further stepof subjecting the finished sur-

13. A METHOD OF MANUFACTURING A MEMBER HAVING A SURFACE THEREON ADAPTEDTO BE SUBJECTED TO EXTREME THERMAL CONDITIONS, SAID METHOD INCLUDING THESTEPS OF FIRST CASTING SAID MEMBER TO INCLUDE AT LEAST ONE INSERTNONFUSIBLE THEREIN AND INTERSECTING SAID SURFACE AND THE FURTHER STEP OFSUBJECTING SAID FINISHED SURFACE TO CYCLIC THERMAL CONDITIONS THEREBYIMMEDIATELY ADJACENT EACH INSERT BY THE COMPRESSIVE UPSETTING OF A LAYEROF SAID MEMBER ADJACENT SAID SURFACE AGAINST EACH INSERT TO PREVENT THEEXTREME THERMAL STRESSES WHICH WOULD OTHERWISE RESULT IN SAID MEMBERADJACENT TO AND INCLUDING SAID SURFACE FROM THE EXTREME THERMALCONDITIONS NORMALLY APPLIED TO SAID SURFACE DURING OPERATIONAL USE OFSAID MEMBER.